The fewer cleriks that knew the better. He simply had his faith in the best man he knew he could control ( father controlling the one clerk whos name i cant remember right now )

The clerics could probably be reasoned with a few hours after missing their doses

With regimes like this you always fear being overthrown from within. So everyone is suspect. You wouldn't allow many people around you. Did you ever see the episode of twilight zone with Peter falk? He leads a rebellion and begins imaging deceit and disloyalty from the people who carried him to power. Same thing here I think.
Also, I don't think the rest of the clerics are capable of such independent thought. Unless told to do something like work together it wouldn't occur to them. Again jealous hoarding of power. Your own downfall.

cos they all fear Christian Bales cheekbones!!!!